The present invention relates to a method of controlling weft yarn insertion in a loom, as well as to a weft yarn deviation brake.
In a method of this type--as disclosed by U.S. Pat. No. 4,962,976--the magnetic core of an electromagnetic linear control system of the yarn deviation brake is shifted, in order to brake the weft yarn by means of the braking element, with a maximum of deviation. As soon as braking with a sharp tension peak occurs towards the end of weft yarn insertion, a high increase in yarn tension takes place due to stopping of the weft yarn drawn from the weft feeder of the loom. The current of the electromagnetic control system is already regulated so that, after a braking, the weft yarn with its reaction force pushes back the braking element, reacting to the braking force, whereby due to smoothing down of the tension peak, there is an absorption of kinetic energy. In other words, the current is regulated so that the braking element which, to start with, is actually shifted with a maximum deviation (i.e. reaches its position of maximum deviation), can subsequently again be moved backward, at least partially, from its position of maximum deviation, due to the reaction force of the yarn, thereby producing a smoothing down effect. Alternatively, due to shifting of the braking element into its position of maximum deviation or rotation, a higher startup current is temporarily set. In both cases, after smoothing down, the yarn deviation or rotation brake takes up again its position of maximum deviation as a result of the braking force.
As disclosed by EP-B-239,055, when the weft yarn is cut at the end of its insertion into the loom, it is known to prevent the weft yarn--which is tensioned by moving of the reed--from bouncing backward as far as the yarn reserve wound on the drum of the weft feeder, that is, to prevent backward oscillations from being produced in the weft yarn, causing the loosening thereof. At the outlet of the weft feeder, in correspondence to the yarn drawing point, there is mounted a yarn deviation element apt to be shifted in a controlled manner along the yarn path, which element, upon cutting of the yarn, is moved into a position of yarn deviation. Friction points are created for the yarn in the position of yarn deviation and the yarn is braked with an increasing braking force, giving rise to a recoil or a spring-back. During weft insertion, the yarn deviation element is kept in a position of no deviation up to the moment of yarn cutting. In any case, this method requires an extremely precise control of the yarn deviation element.